网络状态监听 → ConnectivityManager + Flow

老写法（Java + BroadcastReceiver）

java 复制代码

public class NetworkReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        ConnectivityManager cm = (ConnectivityManager)
                context.getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo info = cm.getActiveNetworkInfo();
        boolean isConnected = info != null && info.isConnected();
        updateNetworkState(isConnected);
    }
}

// 注册
IntentFilter filter = new IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION);
registerReceiver(new NetworkReceiver(), filter);

问题在哪里

NetworkInfo 已废弃（API 29+）。广播接收必须手动注册/解注册，生命周期管理容易泄漏。只能拿到"是否连接"，具体网络类型获取麻烦。

新写法（ConnectivityManager + Flow）

kotlin 复制代码

class NetworkMonitor(context: Context) {

    private val connectivityManager =
        context.getSystemService(Context.CONNECTIVITY_SERVICE) as ConnectivityManager

    val isConnected: Flow<Boolean> = callbackFlow {
        val callback = object : ConnectivityManager.NetworkCallback() {
            override fun onAvailable(network: Network) {
                trySend(true)
            }

            override fun onLost(network: Network) {
                trySend(false)
            }
        }

        val request = NetworkRequest.Builder()
                .addCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET)
                .build()
        connectivityManager.registerNetworkCallback(request, callback)

        // 发送当前状态
        val currentNetwork = connectivityManager.activeNetwork
        val capabilities = connectivityManager.getNetworkCapabilities(currentNetwork)
        trySend(capabilities?.hasCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET) == true)

        awaitClose {
            connectivityManager.unregisterNetworkCallback(callback)
        }
    }
}

// 使用
viewModelScope.launch {
    networkMonitor.isConnected.collect { connected ->
        tvStatus.text = if (connected) "已连接" else "无网络"
    }
}

一句话注意

callbackFlow 是把回调 API 转为 Flow 的标准方式。trySend 在 Flow 里发射元素，awaitClose 在 Flow 被取消时自动执行清理逻辑（解注册 callback），不需要手动管理生命周期。

NetworkRequest.Builder().addCapability() 可以精确过滤网络类型------NET_CAPABILITY_INTERNET 表示该网络能访问互联网，TRANSPORT_WIFI 限制只监听 WiFi。addTransportType 也可以在 Builder 上链式调用组合多个条件。

Java Android 老项目迁移系列，持续更新中。